JP2007214958A - Cv conversion circuit for differential type switched capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a CV conversion circuit for differential type switched capacitor for converting a substantial capacitive difference (signal factor) of two sensor capacitors to a voltage signal with high gain by a first stage operational amplifier even for a differential electrostatic capacitor type sensor with large offset capacity. <P>SOLUTION: In operation of the electron charge transfer, first and second charged sensor capacitors Csa, Csb, and a correction capacitor Coa are separated from a charging voltage source ±Vd and a correction voltage source ±Voc, and the first and second sensor capacitors Csa, Csb and the correction capacitor Coa are connected with an inverting input terminal of an operational amplifier 1. Then, a charged electron charge, in which the first and second sensor capacitors Csa, Csb, and the correction capacitor Coa are added, is transferred to a feed-back capacitor Ccv and a voltage proportional to the added charged electron charge is generated at an output of the operational amplifier 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a differential switched capacitor CV (capacitance / voltage) conversion circuit that performs first-stage signal processing of a differential capacitance sensor applied as various physical quantity sensors, and in particular, a sensor having a large offset capacitance. Even so, the present invention relates to a technical improvement that makes it possible to extract a sensor detection signal with high gain.

=== Principle Switched Capacitor CV Conversion Circuit ===
The basic principle of the switched capacitor CV conversion circuit will be described based on the circuit diagram shown in FIG. In FIG. 1, the capacitance of the sensor capacitor Cs changes according to a physical quantity to be sensed such as pressure and acceleration. One end of the sensor capacitor Cs is connected to a constant positive voltage source Vf. The other end of Cs is connected to a constant negative voltage source −Vd through a switch SW1, and is connected to an inverting input of the operational amplifier 1 through a switch SW2. The non-inverting input of the operational amplifier 1 is connected to the substrate potential Vr. A parallel circuit of the switch SW3 and the feedback capacitor Cc is connected to a feedback path connecting the output of the operational amplifier 1 and the inverting input. The output of the operational amplifier 1 is connected to one end of the output capacitor Ch via the switch SW4. The other end of the output capacitor Ch is connected to the substrate potential Vr.
Here, Cs · Cc · Ch also represents the capacitance value of each capacitor.

The four switches SW1 to SW4 are driven on and off as shown in the waveform diagram attached to FIG. 1 by a control circuit (not shown). The switches SW1 and SW3 have the same phase and are repeatedly turned on and off at a constant cycle. The switch SW2 is turned on for a certain time in the middle of the off periods of SW1 and SW3, and is turned off during other periods. The switch SW4 is turned on for a certain time at the end of the ON period of SW2, and the change points from on to off are aligned with SW2.
While SW1 is on, SW2 is off. During this period, the sensor capacitor Cs is charged to the voltage (Vf + Vd). Since SW3 is also on during this period, the charge on the feedback capacitor Cc is zero.
SW2 is turned on after SW1 and SW3 are turned off. Then, the charge Qs of the sensor capacitor Cs is transferred to the feedback capacitor Cc, and the feedback capacitor Cc is charged to the voltage Vc (Vc = Qs ÷ Cc).
After the charging voltage Vc of the feedback capacitor Cc is stabilized at (Qs ÷ Cc), SW4 is turned on for a short time, the voltage Vc is held in the output capacitor Ch (sample hold), and the smoothed stable DC output voltage Vo. Occurs.

  As is apparent from the above operating principle, the output voltage Vo is proportional to the sensor capacitor Cs as shown in the following equation. The proportionality coefficient increases as the voltage Vd increases, and increases as the feedback capacitor Cc decreases. The greater the proportionality coefficient, the more sensitively the change in sensor capacitor Cs can be detected.

        Vo = (Cs ÷ Cc) × Vd = (Vd ÷ Cc) × Cs

=== Differential capacitance type sensor ===
In order to detect minute changes in physical quantities such as force, acceleration, speed, and displacement with high sensitivity, a differential sensor is often used. In a typical differential capacitance type sensor, one movable electrode is arranged between two fixed electrodes, a first sensor capacitor is formed by the first fixed electrode and the movable electrode, and the second fixed electrode and the movable electrode. Thus, a second sensor capacitor is formed. Then, the two sensor capacitors are arranged such that when the movable electrode is displaced in response to the change in the physical quantity to be detected and the capacitance value of the first sensor capacitor increases, the capacitance value of the second sensor capacitor decreases. The capacitance value of these changes in a complementary manner. In recent years, differential capacitance sensors having a fine structure suitable for various applications have been manufactured by a micro electro mechanical systems (MEMS) technique.

  A circuit for converting a capacitance difference between first and second sensor capacitors of a differential capacitance type sensor into a voltage signal with high sensitivity and high accuracy is a differential switched capacitor which is an object of the present invention. This is a CV conversion circuit.

=== Conventional Differential Switched Capacitor CV Conversion Circuit ===
Two typical configurations of a differential switched capacitor CV conversion circuit that converts a capacitance difference between two sensor capacitors into a voltage signal are shown in FIGS.
First, the circuit of FIG. 2A will be described. Csa is a first sensor capacitor and Csb is a second sensor capacitor. The switches SW1a, SW2b, SW3a, the operational amplifier 1a, and the feedback capacitor Cca have the same configuration as the basic circuit described in FIG. 1, and a voltage signal proportional to the capacitance value of the first sensor capacitor Csa is output to the operational amplifier 1a. Arise. In exactly the same manner, a voltage signal proportional to the capacitance value of the second sensor capacitor Csb is generated at the output of the operational amplifier 1b. The outputs of the operational amplifiers 1a and 1b are input to a differential amplifier composed of an operational amplifier 2 and resistors R1 to R4. The output of the operational amplifier 2 is a voltage signal Vo proportional to the capacitance difference between the first and second sensor capacitors. Occurs.

Next, the circuit of FIG. 2B will be described. A positive constant voltage + Vd is applied to the first sensor capacitor Csa via the switch SW1a, and then the charge of Csa is transferred to the feedback capacitor Cc. 2 After applying a negative constant voltage −Vd to the sensor capacitor Csb, the charge of Csb is transferred to the feedback capacitor Cc, and the output voltage Vo of the operational amplifier 1 is held in the next stage, and then the feedback capacitor Cc is short-circuited by the switch SW3. To do. The above operation is repeated.
Since the applied voltages to the two sensor capacitors Csa and Csb are opposite in polarity and equal in absolute value, if Csa and Csb are equal, the voltage Vo generated at the output of the operational amplifier 1 is zero and there is a difference in capacitance value A voltage Vo proportional to the difference is generated.

  Next, the circuit of FIG. 2C will be described. One end of each of the two sensor capacitors Csa and Csb is directly connected to the non-inverting input of the operational amplifier 1. When the switches SW1 and SW4 are turned on, the switches SW2 and SW3 are turned off, a positive constant voltage + Vd is applied to the other end of the first sensor capacitor Csa, and a negative constant voltage −Vd is applied to the other end of the second sensor capacitor Csb. Applied. When SW1 to SW4 are inverted, a negative constant voltage −Vd is applied to the other end of the first sensor capacitor Csa, and a positive constant voltage + Vd is applied to the other end of the second sensor capacitor Csb. Each time SW1 to SW4 are inverted, SW7 is turned on and off, and the charge that flows into the operational amplifier 1 through the two sensor capacitors Csa and Csb is transferred to the feedback capacitor Cc. As a result, a voltage Vo proportional to the capacitance difference between the two sensor capacitors Csa and Csb is generated at the output of the operational amplifier 1.

  In general, in a circuit system that amplifies a weak signal with low noise, it is important to amplify as much as possible in the first stage circuit that receives the input signal, and then the influence of noise generated in the subsequent stage amplification circuit. Can be reduced. From this point of view, the three types of conventional circuits shown in FIG. 2 are evaluated.

  In the circuit of FIG. 2A, a voltage signal proportional to the capacitance value of the first sensor capacitor Csa and a voltage signal proportional to the capacitance value of the second sensor capacitor Csb are generated, and the difference between the two voltages at the subsequent stage. Is amplified. In this method, when the difference between the absolute values of the capacitance values of Csa and Csb is extremely small, the CV conversion gain of the first operational amplifiers 1a and 1b is limited by the absolute value of Csa and Csb. The voltage signal corresponding to the difference between the capacitance values obtained by the differential amplifier at the next stage is small and will be amplified at the subsequent stage. However, this will increase the influence of noise generated at the amplifier circuit at the subsequent stage.

  On the other hand, in the circuits of FIGS. 2B and 2C, the capacitance difference between the two sensor capacitors Csa and Csb is directly converted into a voltage signal by the operational amplifier 1 in the first stage, and FIG. The above-mentioned problems of the circuit are eliminated in principle, and the signal-to-noise performance is excellent.

  However, for the reality of the differential capacitance type sensor, even in the circuit configurations of FIGS. 2B and 2C, the gain (CV conversion gain) of the first stage circuit that converts the capacitance difference between the two sensor capacitors into a voltage signal. ) Cannot be made large enough.

  The cause is the offset capacitance of the differential capacitance type sensor. When mass-producing a differential capacitance sensor with a fine structure by MEMS technology, it is a reality even though it is designed and manufactured so that the capacitance difference between the two sensor capacitors is zero in the assumed steady state. In mass-produced products, the capacitance difference between the two sensor capacitors varies greatly without becoming zero. Such a capacitance difference between the two sensor capacitors in the steady state is referred to herein as an offset capacitance.

  In a sensor structure based on MEMS, it is difficult to finish a very small capacitance value with high accuracy, and it is inevitable that the offset capacitance varies greatly among individual sensors. In the assumed measurement range, the offset capacitance may even be several to several tens of times the amount of change of the sensor capacitor.

  2B and 2C, the first stage operational amplifier 1 converts the capacitance difference between the sensor capacitors Csa and Csb directly into the voltage signal Vo, which is excellent in terms of signal-to-noise ratio. I mentioned earlier that it was a circuit. However, when there is a large offset capacitance between the two sensor capacitors Csa and Csb, most of the conversion gain of the operational amplifier 1 in the first stage is occupied by the offset capacitance, which is substantially accompanied by a change in the physical quantity to be detected. It becomes impossible to convert a typical capacitance difference (signal component) into a voltage signal with high gain.

  An object of the present invention is to convert a substantial capacitance difference (signal component) between two sensor capacitors into a voltage signal with high gain by a first operational amplifier even in a differential capacitance type sensor having a large offset capacitance. It is to realize a differential switched capacitor CV conversion circuit capable of achieving the above.

=== First Invention ===
The switched capacitor CV conversion circuit of the first invention is specified by the following items (11) to (19).
(11) First and second sensor capacitors, correction capacitors, two charging voltage sources having positive and negative symmetrical potentials, two correction voltage sources having positive and negative symmetrical potentials, an operational amplifier, and an operational amplifier A differential capacitor CV conversion circuit including a feedback capacitor connected between the input and output, a plurality of switches, and a control circuit. (12) Each of the first and second sensor capacitors has one end Are connected to the reference potential, and the other end of each can be connected to a positive / negative charging voltage source via a switch and to the inverting input of an operational amplifier via a switch. (13) Correction capacitor One end is connected to the reference potential, the other end can be connected to a positive / negative correction voltage source via a switch, and can be connected to the inverting input of an operational amplifier via a switch. (14) The operational amplifier has a non-inverting input grounded, and a feedback capacitor is connected between the output and the inverting input. (15) The feedback capacitor can be short-circuited by a switch. (16) (1) Charging operation is performed by alternately connecting positive and negative charging voltages to the first and second sensor capacitors to control the switch so that charging operation, short circuit operation, and charge transfer operation are repeated in sequence. In addition, the positive and negative correction voltage sources are alternately connected to the correction capacitor for charging. (18) The short-circuit operation is to open the feedback capacitor after short-circuiting. (19) The charge transfer operation is the first charge charged. The second sensor capacitor and the correction capacitor are separated from the charging voltage source and the correction voltage source, and the first and second sensor capacitors and the correction capacitor are connected to the inverting input terminal of the operational amplifier. The summed charge stored in the second sensor capacitor and the correction capacitor is transferred to the feedback capacitor, to generate a voltage proportional to the summed charges to the output of the operational amplifier

=== Second Invention ===
The differential switched capacitor CV conversion circuit of the second invention is specified by the following items (21) to (29).
(21) First and second sensor capacitors, correction capacitors, two charging voltage sources having positive and negative symmetrical potentials, two correction voltage sources having positive and negative symmetrical potentials, an operational amplifier, and an operational amplifier A differential switched capacitor CV conversion circuit including a feedback capacitor, a plurality of switches, and a control circuit connected between the input and output of each of the first and second sensor capacitors. Are connected to the reference potential, and the other end of each can be connected to a positive / negative charging voltage source via a switch and to the inverting input of an operational amplifier via a switch. (23) Correction capacitor One end of the operational amplifier is connected to the inverting input of the operational amplifier, and the other end can be switched and connected to a positive / negative correction voltage source via a switch. (24) (25) The feedback capacitor can be short-circuited by a switch. (26) The control circuit controls each switch, charging operation, short-circuit operation, and charge transfer. (27) Charging is performed by alternately connecting positive and negative charging voltages to the first and second sensor capacitors, and alternately connecting positive and negative correction voltage sources to the correction capacitors. (28) The short-circuit operation opens the feedback capacitor after short-circuiting. (29) The charge transfer operation disconnects the charged first and second sensor capacitors from the charging voltage source. Connected to the inverting input terminal of the operational amplifier, the charged charge added by the first and second sensor capacitors and the correction capacitor is transferred to the feedback capacitor, and a voltage proportional to the added charged charge is It is generated at the output of the calculation amplifier

=== Third Invention ===
The differential switched capacitor CV conversion circuit according to the third aspect of the invention is specified by the following items (31) to (39).
(31) First and second sensor capacitors, a correction capacitor, two charging voltage sources having positive and negative symmetrical potentials, a correction voltage source, an operational amplifier, and an operational amplifier connected between input and output A differential switched capacitor CV conversion circuit including a feedback capacitor, a plurality of switches, and a control circuit. (32) Each of the first and second sensor capacitors has one end connected to a reference potential, The other end of the correction capacitor can be connected to a positive / negative charging voltage source via a switch and can be connected to the inverting input of the operational amplifier via a switch. (33) One end of the correction capacitor is connected to the operational amplifier. It is connected to the inverting input, and the other end can be switched to the correction voltage source and the ground potential via a switch. (34) The operational amplifier is grounded at the non-inverting input and fed back between the output and the inverting input (35) The feedback capacitor can be short-circuited by a switch. (36) The control circuit controls each switch so that a charging operation, a short-circuiting operation, and a charge transfer operation are sequentially repeated. (37) In the charging operation, positive and negative charging voltages are alternately connected to the first and second sensor capacitors for charging, and the correction capacitor is connected to the ground potential and then connected to the correction voltage source for charging. (38) The short-circuit operation is to open the feedback capacitor after short-circuiting. (39) The charge transfer operation is to invert the operational amplifier after disconnecting the charged first and second sensor capacitors from the charging voltage source. Connected to the input terminal, the added charge of the first and second sensor capacitors and the correction capacitor is transferred to the feedback capacitor, and a voltage proportional to the added charge is supplied to the operational amplifier. It is generated to force

  As described above, in the differential capacitance type sensor, even if the input of the physical quantity to be detected is zero, the capacitance values of the first and second sensor capacitors are not necessarily equal, and a considerably large difference occurs. There are many things. The capacitance difference between the first and second sensor capacitors when the input of the detected physical quantity is zero is referred to as offset capacitance.

  The differential switched capacitor CV conversion circuit according to the present invention cancels the offset capacitance of the first and second sensor capacitors by the correction capacitor and the correction voltage source, and outputs the operational amplifier when the input of the detected physical quantity is zero. The voltage is configured to be almost zero.

  The offset capacities of the first and second sensor capacitors are different for each differential capacitance type sensor. In the present invention, at the final stage of the production process of each differential switched capacitor CV conversion circuit, the offset capacitance of the differential capacitance type sensor (first and second sensor capacitors) actually connected to the circuit is calculated. The voltage of the correction voltage source is adjusted and set so that the offset capacitance is canceled by the correction capacitor and the correction voltage source.

=== Embodiment of the first invention ===
FIG. 3 shows a circuit configuration of the embodiment of the first invention.
(A) This differential switched capacitor CV conversion circuit includes first and second sensor capacitors Csa and Csb, a correction capacitor Coa, two charging voltage sources ± Vd having positive and negative symmetrical potentials, and positive and negative Two correction voltage sources ± Voc having symmetrical potentials, an operational amplifier 1, a feedback capacitor Ccv connected between the input and output of the operational amplifier 1, a plurality of switches SW1 to SW7 and SWa to SWc, and a control circuit ( (Not shown).

(A) One end of each of the first and second sensor capacitors Csa and Csb is connected to a reference potential, and the other end can be connected to a positive / negative charging voltage source ± Vd via the switches SW1 to SW4. And can be connected to the inverting input of the operational amplifier 1 via the switches SW5 and SW6.

(C) One end of the correction capacitor Coa is connected to the reference potential, and the other end can be connected to the positive / negative correction voltage source ± Voc via the switches SWa and SWb. Can be connected to inverting input.
(D) The operational amplifier 1 has a non-inverting input grounded, and a feedback capacitor Ccv is connected between the output and the inverting input.
(E) The feedback capacitor Ccv can be short-circuited by the switch SW7.

(F) The control circuit controls the switches SW1 to SW7 and SWa to SWc as shown in the timing chart, and sequentially repeats the charging operation, the short circuit operation, and the charge transfer operation.

(G) Charging operation is performed by alternately charging positive and negative charging voltages ± Vd to the first and second sensor capacitors Csa and Csb and alternately charging positive and negative correction voltage sources ± Voc to the correction capacitor Coa. Connect and charge.
(G) In the short-circuit operation, the feedback capacitor Ccv is short-circuited and then opened.

(G) The charge transfer operation is performed by separating the charged first and second sensor capacitors Csa and Csb and the correction capacitor Coa from the charging voltage source ± Vd and the correction voltage source ± Voc, and the first and second sensor capacitors Csa. Csb and the correction capacitor Voa are connected to the inverting input terminal of the operational amplifier 1, and the added charge of the first and second sensor capacitors Csa and Csb and the correction capacitor Coa is transferred to the feedback capacitor Ccv, and the added charge A voltage proportional to the charge is generated at the output of the operational amplifier 1.

(E) The output of the operational amplifier 1 is detected in synchronization with SW1 to SW7 and SWa to SWc by a synchronous detection circuit (capacitor C8, switch SW8, switch SW9, capacitor C9, voltage follower 3) and doubled. The output voltage Vo is continuously converted.

=== Embodiment of the Second Invention ===
FIG. 4 shows a circuit configuration of an embodiment of the second invention.
(A) This differential switched capacitor CV conversion circuit includes first and second sensor capacitors Csa and Csb, a correction capacitor Coa, two charging voltage sources ± Vd having positive and negative symmetrical potentials, and positive and negative Two correction voltage sources ± Voc having symmetrical potentials, an operational amplifier 1, a feedback capacitor Ccv connected between the input and output of the operational amplifier 1, a plurality of switches SW1 to SW7, SWa, SWb, and a control circuit ( (Not shown).

(A) One end of each of the first and second sensor capacitors Csa and Csb is connected to a reference potential, and the other end can be connected to a positive / negative charging voltage source ± Vd via the switches SW1 to SW4. And can be connected to the inverting input of the operational amplifier 1 via the switches SW5 and SW6.

(C) One end of the correction capacitor Coa is connected to the inverting input of the operational amplifier 1, and the other end can be switched and connected to the positive / negative correction voltage source ± Voc via the switches SWa and SWb.

(D) The operational amplifier 1 has a non-inverting input grounded, and a feedback capacitor Ccv is connected between the output and the inverting input.
(E) The feedback capacitor Ccv can be short-circuited by the switch SW7.

(F) The control circuit controls the switches SW1 to SW7, SWa, and SWb, and sequentially repeats the charging operation, the short circuit operation, and the charge transfer operation.
(G) Charging operation is performed by alternately charging positive and negative charging voltages ± Vd to the first and second sensor capacitors Csa and Csb and alternately charging positive and negative correction voltage sources ± Voc to the correction capacitor Coa. Connect and charge.
(G) In the short-circuit operation, the feedback capacitor Cov is short-circuited and then released.

(G) In the charge transfer operation, the charged first and second sensor capacitors Csa and Csb are disconnected from the charging voltage source ± Vd, and then connected to the inverting input of the operational amplifier 1 to obtain the first and second sensor capacitors Csa. Transfer the added charge of Csb and correction capacitor Coa to the feedback capacitor Ccv, and generate a voltage proportional to the added charge at the output of the operational amplifier 1.

(E) The output of the operational amplifier 1 is detected in synchronization with SW1 to SW7 and SWa to SWc by a synchronous detection circuit (capacitor C8, switch SW8, switch SW9, capacitor C9, voltage follower 3) and doubled. The output voltage Vo is continuously converted.

=== Embodiment of the Third Invention ===
FIG. 5 shows a circuit configuration of an embodiment of the third invention.
(A) This differential switched capacitor CV conversion circuit includes first and second sensor capacitors Csa and Csb, a correction capacitor Coa, two charging voltage sources ± Vd having positive and negative symmetrical potentials, and correction A voltage source + Voc, an operational amplifier 1, a feedback capacitor Ccv connected between the input and output of the operational amplifier 1, a plurality of switches SW1 to SW7, SWa, and SWb, and a control circuit (not shown) are provided.

(A) One end of each of the first and second sensor capacitors Csa and Csb is connected to a reference potential, and the other end can be connected to a positive / negative charging voltage source ± Vd via the switches SW1 to SW4. And can be connected to the inverting input of the operational amplifier 1 via the switches SW5 and SW6.

(C) One end of the correction capacitor Coa is connected to the inverting input of the operational amplifier 1, and the other end can be switched and connected to the correction voltage source + Voc and the ground potential via the switches SWa and SWb.
(D) The operational amplifier 1 has a non-inverting input grounded, and a feedback capacitor Ccv is connected between the output and the inverting input.
(E) The feedback capacitor Ccv can be short-circuited by the switch SW7.

(F) The control circuit controls the switches SW1 to SW7, SWa, and SWb, and sequentially repeats the charging operation, the short circuit operation, and the charge transfer operation.
(G) The charging operation is performed by charging the first and second sensor capacitors Csa and Csb by alternately connecting positive and negative charging voltages ± Vd and connecting the correction capacitor Coa to the ground potential and then correcting the voltage source. Connect + Voc and charge.
(G) In the short-circuit operation, the feedback capacitor Cov is short-circuited and then released.

(G) In the charge transfer operation, the charged first and second sensor capacitors Csa and Csb are disconnected from the charging voltage source ± Vd, and then connected to the inverting input of the operational amplifier 1 to obtain the first and second sensor capacitors Csa. Transfer the added charge of Csb and correction capacitor Coa to the feedback capacitor Ccv, and generate a voltage proportional to the added charge at the output of the operational amplifier 1.

(E) The output of the operational amplifier 1 is detected in synchronization with SW1 to SW7 and SWa to SWc by a synchronous detection circuit (capacitor C8, switch SW8, switch SW9, capacitor C9, voltage follower 3) and doubled. The output voltage Vo is continuously converted.

It is a block diagram of a fundamental switched capacitor CV conversion circuit. It is a block diagram of the conventional differential type switched capacitor CV conversion circuit. 1 is a configuration diagram of a differential switched capacitor CV conversion circuit according to a first invention. FIG. It is a block diagram of the differential switched capacitor CV conversion circuit based on 2nd invention. It is a block diagram of the differential switched capacitor CV conversion circuit based on 3rd invention.

Explanation of symbols

1 operational amplifier Csa / Csb first / second sensor capacitor Coa correction capacitor ± Vd charge voltage source ± Voc correction voltage source Ccv feedback capacitor SW1 to SW7 / SWa / SWb / SWc switch

Claims (3)

First and second sensor capacitors, correction capacitors, two charging voltage sources having positive and negative symmetrical potentials, two correction voltage sources having positive and negative symmetrical potentials, an operational amplifier, and input / output of the operational amplifier A differential switched capacitor CV conversion circuit including a feedback capacitor connected in between, a plurality of switches, and a control circuit;
One end of each of the first and second sensor capacitors is connected to a reference potential, and the other end of each of the first and second sensor capacitors can be connected to a positive / negative charging voltage source via a switch, and an operational amplifier via a switch. Can be connected to the inverting input,
The correction capacitor has one end connected to a reference potential, the other end can be connected to a positive / negative correction voltage source via a switch, and can be connected to an inverting input of an operational amplifier via a switch.
The operational amplifier has a non-inverting input grounded, a feedback capacitor connected between the output and the inverting input,
The feedback capacitor can be short-circuited by a switch,
The control circuit controls each switch so that the charging operation, the short-circuit operation, and the charge transfer operation are sequentially repeated.
The charging operation is performed by alternately connecting positive and negative charging voltages to the first and second sensor capacitors, and charging the correction capacitor by alternately connecting positive and negative correction voltage sources.
Short-circuit operation shorts the feedback capacitor and then opens it,
In the charge transfer operation, the charged first and second sensor capacitors and the correction capacitor are disconnected from the charging voltage source and the correction voltage source, and the first and second sensor capacitors and the correction capacitor are connected to the inverting input of the operational amplifier. A differential switched capacitor CV conversion circuit that transfers the added charge of the first and second sensor capacitors and the correction capacitor to the feedback capacitor and generates a voltage proportional to the added charge at the output of the operational amplifier. . First and second sensor capacitors, correction capacitors, two charging voltage sources having positive and negative symmetrical potentials, two correction voltage sources having positive and negative symmetrical potentials, an operational amplifier, and input / output of the operational amplifier A differential switched capacitor CV conversion circuit including a feedback capacitor connected in between, a plurality of switches, and a control circuit;
One end of each of the first and second sensor capacitors is connected to a reference potential, and the other end of each of the first and second sensor capacitors can be connected to a positive / negative charging voltage source via a switch, and an operational amplifier via a switch. Can be connected to the inverting input,
One end of the correction capacitor is connected to the inverting input of the operational amplifier, and the other end can be switched to a positive / negative correction voltage source via a switch.
The operational amplifier has a non-inverting input grounded, a feedback capacitor connected between the output and the inverting input,
The feedback capacitor can be short-circuited by a switch,
The control circuit controls each switch so that the charging operation, the short-circuit operation, and the charge transfer operation are sequentially repeated.
The charging operation is performed by alternately connecting positive and negative charging voltages to the first and second sensor capacitors, and charging the correction capacitor by alternately connecting positive and negative correction voltage sources.
Short-circuit operation shorts the feedback capacitor and then opens it,
In the charge transfer operation, the charged first and second sensor capacitors are disconnected from the charging voltage source, connected to the inverting input of the operational amplifier, and the added charge charges of the first and second sensor capacitors and the correction capacitor are added. A differential switched capacitor CV conversion circuit that transfers voltage to the feedback capacitor and generates a voltage proportional to the added charge charge at the output of the operational amplifier. A first and a second sensor capacitor, a correction capacitor, two charging voltage sources having positive and negative symmetrical potentials, a correction voltage source, an operational amplifier, and a feedback capacitor connected between the input and output of the operational amplifier; A differential switched capacitor CV conversion circuit including a plurality of switches and a control circuit,
One end of each of the first and second sensor capacitors is connected to a reference potential, and the other end of each of the first and second sensor capacitors can be connected to a positive / negative charging voltage source via a switch, and the operational amplifier can be connected via a switch. Can be connected to the inverting input,
One end of the correction capacitor is connected to the inverting input of the operational amplifier, and the other end can be switched and connected to the correction voltage source and the ground potential via a switch.
The operational amplifier has a non-inverting input grounded, a feedback capacitor connected between the output and the inverting input,
The feedback capacitor can be short-circuited by a switch,
The control circuit controls each switch, and sequentially repeats the charging operation, the short-circuiting operation, and the charge transfer operation,
The charging operation is performed by alternately connecting positive and negative charging voltages to the first and second sensor capacitors and charging the correction capacitor by connecting the correction capacitor to the ground potential and then connecting to the correction voltage source.
In short-circuit operation, the feedback capacitor is short-circuited and then opened.
In the charge transfer operation, the charged first and second sensor capacitors are disconnected from the charging voltage source, connected to the inverting input of the operational amplifier, and the added charge charges of the first and second sensor capacitors and the correction capacitor are added. A differential switched capacitor CV conversion circuit that transfers a voltage to the feedback capacitor and generates a voltage proportional to the added charge at the output of the operational amplifier.

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